Yeah it's from lack of nitrogen, too much nitrogen in your plants makes it harsh and the gassing off during drying much more harsh (you get that planty smell). Try growing with some super soil and do it natural and organic like its meant to be done you see a lot more of the plants natural beauty not just yellowing but purpling redding and other beautiful colors that come with growing plants natural like they are meant to be grown outdoors. My golden goat looks so Hawaiian when finished yellowing of leaves around lime green buds really awesome at the end and the harvests are not reduced but much at all if anything I think they are better cause the taste is amazing. Basically what I am saying is that if your plant is nice and green with lots of green fan leaves at the end it might look healthy but it's not grown properly you want some fading at the end to release that extra nitrogen, your bloom fertilizers are very low in nitrogen but even those contain too much that's why I stopped using those you can get better fertilizers than premade ones that are watered downed and contain excessive levels of salt.